1. Describe the functions of blood.
A. Blood: is a liquid connective tissue that consists of cells surrounded by a liquid extracellular matrix. The
... [Show More] extracellular matrix is called blood plasma, and it suspends various cells and cell fragments.
B. interstitial fluid: is the fluid that bathes body cells and is constantly renewed by the blood.
C. functions of blood: Blood transports oxygen from the lungs and nutrients from the gastrointestinal tract, which diffuse from the blood into the interstitial fluid and then into body cells. Carbon dioxide and other wastes move in the reverse direction, from body cells to interstitial fluid to blood. Blood then transports the wastes to various organs—the lungs, kidneys, and skin—for elimination from the body. The blood has the following 3 general functions.
I. Transportation: blood transports oxygen from the lungs to the cells of the body and carbon dioxide from the body cells to the lungs for exhalation. It carries nutrients from the gastrointestinal tract to body cells and hormones from endocrine glands to other body cells. Blood also transports heat and waste products to various organs for elimination from the body.
II. Regulation: Circulating blood helps maintain homeostasis of all body fluids. Blood helps regulate pH through the use of buffers (chemicals that convert strong acids or bases into weak ones). It also helps adjust body temperature through the heat-absorbing and coolant properties of the water in blood plasma and its variable rate of flow through the skin, where excess heat can be lost from the blood to the environment. In addition, blood osmotic pressure influences the water content of cells, mainly through interactions of dissolved ions and proteins.
III. Protection: Blood can clot, which protects against its excessive loss from the cardiovascular system after an injury. In addition, its white blood cells protect against disease by carrying on phagocytosis. Several types of blood proteins, including antibodies, interferons, and complement, help protect against disease in a variety of ways.
2. Describe the physical characteristics and principal components of blood.
A. physical characteristics of blood: Blood is denser and more viscous (thicker) than water and feels slightly sticky. The temperature of blood is 38C (100.4F), about 1C higher than oral or rectal body temperature, and it has a slightly alkaline pH ranging from 7.35 to 7.45. The color of blood varies with its oxygen content. When saturated with oxygen, it is bright red. When unsaturated with oxygen, it is dark red. Blood constitutes about 20% of extracellular fluid, amounting to 8% of the total body mass. The blood volume is 5 to 6 liters (1.5 gal) in an average- sized adult male and 4 to 5 liters (1.2 gal) in an average-sized adult female. The gender difference in volume is due to differences in body size. Several hormones, regulated by negative feedback, ensure that blood volume and osmotic pressure remain relatively constant. Especially important are the hormones aldosterone, antidiuretic hormone, and atrial natriuretic peptide, which regulate how much water is excreted in the urine
3. List the major components of plasma and explain their importance.
A. components of blood: Whole blood has two components: (1) blood plasma, a watery liquid extracellular matrix that contains dissolved substances, and (2) formed elements, which are cells and cell fragments. If a sample of blood is centrifuged (spun) in a small glass tube, the cells (which are more dense) sink to the bottom of the tube while the plasma (which is less dense) forms a layer on top. Blood is about 45% formed elements and 55% blood plasma. Normally, more than 99% of the formed elements are cells named for their red color—red blood cells (RBCs). Pale, colorless white blood cells (WBCs) and platelets occupy less than 1% of the formed elements.
I. buffy coat: since white blood cells and platelets that occupy less than 1% of blood are less dense than red blood cells and more dense than blood plasma they create this coating between the red blood cells and blood plasma in centrifuged blood.
II. Plasma: Blood plasma is about 91.5% water and 8.5% solutes, most of which are proteins.
a. plasma proteins: proteins that are confined to blood and not found elsewhere in the body. Most of these proteins are synthesized by hepatocytes (liver cells). Responsible for colloid osmotic pressure. Major contributors to blood viscosity. Transport hormones (steroid), fatty acids, and calcium. Help regulate blood pH.
b. Albumins: account for 54% of plasma proteins. It is the smallest and most numerous plasma protein. It help maintain osmotic pressure, an important factor in the exchange of fluids across blood capillary walls.
c. Globulins: account for 38% of plasma proteins. They are large proteins (plasma cells produce immunoglobulins. Immunoglobulins help attack viruses and bacteria. Alpha and beta globulins transport iron, lipids, and fat-soluble vitamins.
d. Fibrinogen: account for 7% of plasma proteins and are large proteins. Plays essential role in blood clotting.
e. antibodies or immunoglobulins: Certain blood cells develop into cells that produce gamma globulins, an important type of globulin. because they are produced during certain immune responses. Foreign substances (antigens) such as bacteria and viruses stimulate production of millions of different types of these cells. This type of cell binds specifically to the antigen that stimulated its production and thus disables the invading antigen.
III. formed elements: include three principal components: red blood cells, white blood cells, and platelets
a. red blood cells (RBCs): erythrocytes transport oxygen from the lungs to body cells and deliver carbon dioxide from body cells to the lungs.
b. white blood cells (WBCs): leukocytes protect the body from invading pathogens and other foreign substances. There are several types of these cells: neutrophils, basophils, eosinophils, monocytes, and lymphocytes. Lymphocytes are further subdivided into B lymphocytes (B cells), T lymphocytes (T cells), and natural killer (NK) cells. Each type of this cell contributes in its own way to the body’s defense mechanisms.
c. Platelets: the final type of formed element, are fragments of cells that do not have a nucleus. Among other actions, they release chemicals that promote blood clotting when blood vessels are damaged. They are the functional equivalent of thrombocytes, nucleated cells found in lower vertebrates that prevent blood loss by clotting blood.
IV. Hematocrit: is the percentage of total blood volume occupied by red blood cells. A value of 40 indicates that 40% of the volume of blood is composed of RBCs. The normal range of hematocrit for adult females is 38–46% (average = 42); for adult males, it is 40–54% (average = 47). The hormone testosterone, present in much higher concentration in males than in females, stimulates synthesis of erythropoietin (EPO), the hormone that in turn stimulates production of RBCs. Thus, testosterone contributes to higher values in males. Lower values in women during their reproductive years also may be due to excessive loss of blood during menstruation. A significant drop in these values indicates anemia, a lower-than-normal number of RBCs.
V. Polycythemia: the percentage of RBCs is abnormally high, and the hematocrit may be 65% or higher. This raises the viscosity of blood, which increases the resistance to flow and makes the blood more difficult for the heart to pump. Increased viscosity also contributes to high blood pressure and increased risk of stroke. Causes of polycythemia include abnormal increases in RBC production, tissue hypoxia, dehydration, and blood doping or the use of EPO by athletes.
4. Explain the origin of blood cells.
A. formation of blood cells:
I. hemopoiesis or hematopoiesis: The process by which the elements of blood develop. Before birth, the elements of blood first occurs in the yolk sac of an embryo and later in the liver, spleen, thymus, and lymph nodes of a fetus. Red bone marrow becomes the primary site in which elements of blood develop in the last 3 months before birth, and continues as the source of blood cells after birth and throughout life.
II. red bone marrow: is a highly vascularized connective tissue located in the microscopic spaces between trabeculae of spongy bone tissue. It is present chiefly in bones of the axial skeleton, pectoral and pelvic girdles, and the proximal epiphyses of the humerus and femur.
III. pluripotent stem cells: is composed of 0.05% to 0.1% of red bone marrow cells. Can be referred to hemocytoblasts and are derived from mesenchyme (tissue from which almost all connective tissues develop). These cells have the capacity to develop into many different types of cells. In newborns, all bone marrow is red and thus active in blood cell production. As an individual ages, the rate of blood cell formation decreases; red bone marrow in the medullary (marrow) cavity of long bones becomes inactive and is replaced by yellow bone marrow, which consists largely of fat cells. Under certain conditions, such as severe bleeding, yellow bone marrow can revert to red bone marrow; this occurs as blood-forming stem cells from red bone marrow move into yellow bone marrow, which is then repopulated by these stem cells. In order to form blood cells, these stem cells in red bone marrow produce two further types of stem cells, which have the capacity to develop into several types of cells. These stem cells are called myeloid stem cells and lymphoid stem cells. Myeloid stem cells begin their development in red bone marrow and give rise to red blood cells, platelets, monocytes, neutrophils, eosinophils, basophils, and mast cells. Lymphoid stem cells, which give rise to lymphocytes, begin their development in red bone marrow but complete it in lymphatic tissues Lymphoid stem cells also give rise to natural killer (NK) cells. Although the various stem cells have distinctive cell identity markers in their plasma membranes, they cannot be distinguished histologically and resemble lymphocytes.
IV. progenitor cells: a possible derivative from myeloid stem cells. are no longer capable of
reproducing themselves and are committed to giving rise to more specific elements of blood. Some of these cells are known as colony-forming units (CFUs). Following the CFU designation is an abbreviation that indicates the mature elements in blood that they will produce: CFU–E ultimately produces erythrocytes (red blood cells); CFU–Meg produces megakaryocytes, the source of platelets; and CFU–GM ultimately produces granulocytes (specifically, neutrophils) and monocytes. Progenitor cells, like stem cells, resemble lymphocytes and cannot be distinguished by their microscopic appearance alone.
V. precursor cells or blasts: Over several cell divisions they develop into the actual formed elements of blood. For example, mono- blasts develop into monocytes, eosinophilic myeloblasts develop into eosinophils, and so on. Precursor cells have recognizable microscopic appearances.
VI. hemopoietic growth factors: regulate the differentiation and proliferation of particular progenitor cells.
VII. erythropoietin or EPO: Increases the number of red blood cell precursors. Are produced primarily by cells in the kidneys that lie between the kidney tubules (peritubular interstitial cells). With renal failure, their release slows and RBC production is inadequate. This leads to a decreased hematocrit, which leads to a decreased ability to deliver oxygen to body tissues.
VIII. thrombopoietin or TPO: is a hormone produced by the liver that stimulates the formation of platelets from megakaryocytes. Several different cytokines regulate development of different blood cell types.
IX. Cytokines: Are small glycoproteins that are typically produced by cells such as red bone marrow cells, leukocytes, macrophages, fibroblasts, and endothelial cells. They generally act as local hormones. Also, they stimulate proliferation of progenitor cells in red bone marrow and regulate the activities of cells involved in nonspecific defenses (such as phagocytes) and immune responses (such as B cells and T cells).
X. colony stimulating factors (CSFs): an important family of cytokines that stimulate white blood cell formation.
XI. Interleukins: along with CSFs is another main family of cytokines that stimulate white blood cell formation.
5. Describe the structure, functions, life cycle and production of red blood cells.
A. red blood cells or erythrocytes:
I. Hemoglobin: which is a pigment that gives whole blood its red color. A healthy adult male has about 5.4 million red blood cells per microliter (µL) of blood,* and a healthy adult female has about
4.8 million. (One drop of blood is about 50 µL.) To maintain normal numbers of RBCs, new mature cells must enter the circulation at the astonishing rate of at least 2 million per second, a pace that balances the equally high rate of RBC destruction.
II. RBC anatomy: are biconcave discs with a diameter of 7–8 µm. (Recall that 1 µm = 1/25,000 of an inch or 1/10,000 of a centimeter or 1/1000 of a millimeter.) Mature red blood cells have a simple structure. Their plasma membrane is both strong and flexible, which allows them to deform without rupturing as they squeeze through narrow blood capillaries. As you will see later, certain glycolipids in the plasma membrane of RBCs are antigens that account for the various blood groups such as the ABO and Rh groups. RBCs lack a nucleus and other organelles and can neither reproduce nor carry on extensive metabolic activities. The cytosol of RBCs contains hemoglobin molecules; these important molecules are synthesized before loss of the nucleus during RBC production and constitute about 33% of the cell’s weigh
III. RBC physiology: Red blood cells are highly specialized for their oxygen transport function. Because mature RBCs have no nucleus, all of their internal space is available for oxygen transport. Because RBCs lack mitochondria and generate ATP anaerobically (without oxygen), they do not use up any of the oxygen they transport. Even the shape of an RBC facilitates its function. A biconcave disc has a much greater surface area for the diffusion of gas molecules into and out of the RBC than would, say, a sphere or a cube.
a. Globin: a component that composes hemoglobin. Is made up of four polypeptide chains (two alpha and two beta chains). CO2 is absorbed by the amino acid part of the hemoglobin and then releases carbon dioxide as blood flows through the lungs, the carbon dioxide is released from hemoglobin and then exhaled.
b. Heme: a component that composes hemoglobin. A ringlike non-protein pigment that is bound to each of the 4 chains. At the center of each heme ring is and iron ion (Fe2+) that can combine reversibly with a oxygen molecule. This makes it possible for a hemoglobin molecule to bind to 4 oxygen molecules. Each oxygen molecule picked up from the lungs is bound to an iron ion. As blood flows through tissue capillaries, the iron–oxygen reaction reverses. Hemoglobin releases oxygen, which diffuses first into the interstitial fluid and then into cells.
c. nitric oxide (NO): Is produced by the endothelial cells that line blood vessels, binds to hemoglobin. Under some circumstances, hemoglobin releases this molecule. The released of this molecule causes vasodilation, an increase in blood vessel diameter that occurs when the smooth muscle in the vessel wall relaxes. Vasodilation improves blood flow and enhances oxygen delivery to cells near the site of this molecules release.
IV. RBC life cycle: Red blood cells live only about 120 days because of the wear and tear their plasma membranes undergo as they squeeze through blood capillaries. Without a nucleus and other organelles, RBCs cannot synthesize new components to replace damaged ones. The plasma membrane becomes more fragile with age, and the cells are more likely to burst, especially as they squeeze through narrow channels in the spleen. Ruptured red blood cells are removed from circulation and destroyed by fixed phagocytic macrophages in the spleen and liver, and the breakdown products are recycled and used in numerous metabolic processes, including the formation of new red blood cells. The recycling occurs as follows
1) Macrophages in the spleen, liver, or red bone marrow phagocytize ruptured and worn- out red blood cells.
2) The globin and heme portions of hemoglobin are split apart.
3) Globin is broken down into amino acids, which can be reused to synthesize other
proteins.
4) Iron is removed from the heme portion in the form of Fe3+, which associates with the plasma protein transferrin , a transporter for Fe3+ in the bloodstream.
5) In muscle fibers, liver cells, and macrophages of the spleen and liver, Fe3+ detaches from transferrin and attaches to an iron-storage protein called ferritin.
6) On release from a storage site or absorption from the gastrointestinal tract, Fe3+ reattaches to transferrin.
7) The Fe3+ transferrin complex is then carried to red bone marrow, where RBC precursor cells take it up through receptor- mediated endocytosis for use in hemoglobin synthesis. Iron is needed for the heme portion of the hemoglobin molecule, and amino acids are needed for the globin portion. Vitamin B12 is also needed for the synthesis of hemoglobin.
8) Erythropoiesis in red bone marrow results in the production of red blood cells, which enter the circulation.
9) When iron is removed from heme, the non-iron portion of heme is converted to biliverdin, a green pigment, and then into bilirubin, a yellow- orange pigment.
10) Bilirubin enters the blood and is transported to the liver.
11) Within the liver, bilirubin is released by liver cells into bile, which passes into the small intestine and then into the large intestine.
12) In the large intestine, bacteria convert bilirubin into urobilinogen.
13) Some urobilinogen is absorbed back into the blood, converted to a yellow pigment called urobilin, and excreted in urine.
14) Most urobilinogen is eliminated in feces in the form of a brown pigment called stercobilin, which gives feces its characteristic color.
a. Transferrin: a transporter of Fe3+ in the blood stream.
b. Ferritin: An iron storage protein in which Fe3+ transfers to after it detaches from transferrin.
c. Bilirubin: a yellow-orange pigment. is released by liver cells into bile, which passes into the small intestine and then into the large intestine. In the large intestine, bacteria convert this into urobilinogen.
V. Erythropoiesis: the production of RBCs, starts in the red bone marrow with a precursor cell called a proerythroblast. The proerythroblast divides several times, producing cells that begin to synthesize hemoglobin. Normally, the formation of RBCs and red blood cell destruction proceed at roughly the same pace. If the oxygen-carrying capacity of the blood falls because production is not keeping up with RBC destruction, a negative feedback system steps up RBC production. The controlled condition is the amount of oxygen delivered to body tissues.
VI. Reticulocyte: Near the end of the development of RBCs The nucleus is ejected from the cell. Loss of the nucleus causes the center of the cell to indent, producing the red blood cell’s distinctive biconcave shape. These cells retain some mitochondria, ribosomes, and endoplasmic reticulum. They pass from red bone marrow into the bloodstream by squeezing between the endothelial cells of blood capillaries. They develop into mature red blood cells within 1 to 2 days after their release from red bone marrow.
VII. Hypoxia: is cellular oxygen deficiency. It may occur if too little oxygen enters the blood. For example, the lower oxygen content of air at high altitudes reduces the amount of oxygen in the blood. Oxygen delivery may also fall due to anemia, which has many causes: Lack of iron, lack of certain amino acids, and lack of vitamin B12 are but a few. Circulatory problems that reduce blood flow to tissues may also reduce oxygen delivery. Whatever the cause, cellular oxygen deficiency stimulates the kidneys to step up the release of erythropoietin, which speeds the development of proerythroblasts into reticulocytes in the red bone marrow. As the number of circulating RBCs increases, more oxygen can be delivered to body tissues.
6. Describe the structure, functions and production of white blood cells.
A. white blood cells or leukocytes: They have nuclei and a full complement of other organelles but they do not contain hemoglobin. They are classified as either granular or agranular, depending on whether they contain conspicuous chemical-filled cytoplasmic granules (vesicles) that are made visible by staining when viewed
through a light microscope. Granular leukocytes include neutrophils, eosinophils, and basophils; agranular leukocytes include lymphocytes and monocytes. Monocytes and granular leukocytes develop from myeloid stem cells. In contrast, lymphocytes develop from lymphoid stem cells.
I. granular leukocytes: After staining, each of the three types of granular leukocytes displays conspicuous granules with distinctive coloration that can be recognized under a light microscope. Granular leukocytes can be distinguished as follows:
a. Eosinophil: The large, uniform-sized granules within this type of granular leukocyte (eosin-loving)— they stain red-orange with acidic dyes. The granules usually do not cover or obscure the nucleus, which most often has two lobes connected by either a thin strand or a thick strand of nuclear material.
b. Basophil: The round, variable-sized granules this type of granular leukocyte (= basic loving)—they stain blue- purple with basic dyes. The granules commonly obscure the nucleus, which has two lobes.
c. Neutrophil: are smaller than those of other granular leukocytes, evenly distributed, and pale lilac. Because the granules do not strongly attract either the acidic (red) or basic (blue) stain, these WBCs are neutral loving. The nucleus has two to five lobes, connected by very thin strands of nuclear material. As the cells age, the number of nuclear lobes increases. Because older cells thus have several differently shaped nuclear lobes, they are often called polymorphonuclear leukocytes (PMNs), polymorphs, or “polys.”
II. agranular leukocytes: possess cytoplasmic granules, the granules are not visible under a light microscope because of their small size and poor staining qualities.
a. Lymphocyte: stains dark and is round or slightly indented. The cytoplasm stains sky blue and forms a rim around the nucleus. The larger the cell, the more cytoplasm is visible. Lymphocytes are classified by cell diameter as large lymphocytes (10– 14 µm) or small lymphocytes (6–9 µm). Although the functional significance of the size difference between small and large lymphocytes is unclear, the distinction is still clinically useful because an increase in the number of large lymphocytes has diagnostic significance in acute viral infections and in some immunodeficiency diseases. They function by continually move among lymphoid tissues, lymph, and blood, spending only a few hours at a time in blood. Thus, only a small proportion of the total lymphocytes are present in the blood at any given time. Three main types of lymphocytes are B cells, T cells, and natural killer (NK) cells. B cells are particularly effective in destroying bacteria and inactivating their toxins. T cells attack viruses, fungi, transplanted cells, cancer cells, and some bacteria, and are responsible for transfusion reactions, allergies, and the rejection of transplanted organs. Immune responses carried out by both B cells and T cells help combat infection and provide protection against some diseases. Natural killer cells attack a wide variety of infectious microbes and certain spontaneously arising tumor cells.
b. Monocyte: is usually kidney-shaped or horseshoe-shaped, and the cytoplasm is blue- gray and has a foamy appearance. The cytoplasm’s color and appearance are due to very fine azurophilic granules, which are lysosomes. Blood is merely a conduit for monocytes, which migrate from the blood into the tissues, where they enlarge and differentiate into macrophages. Functionally they take longer to reach a site of infection than neutrophils, but they arrive in larger numbers and destroy more microbes. On their arrival, monocytes enlarge and differentiate into wandering macrophages, which clean up cellular debris and microbes by phagocytosis after an infection.
c. Macrophage: Large eaters
d. fixed macrophage: which means they reside in a particular tissue; examples are alveolar macrophages in the lungs or macrophages in the spleen.
e. wandering macrophage: Others become wandering macrophages, which roam the
tissues and gather at sites of infection or inflammation.
f. major histocompatibility (MHC) antigens: white blood cells and all other nucleated cells in the body have this protein protruding from their plasma membrane into the extracellular fluid. These “cell identity markers” are unique for each person (except identical twins). Although RBCs possess blood group antigens, they lack the MHC antigens.
III. WBC physiology:
a. Leukocytosis: an increase in the number of WBCs above 10,000/µL, is a normal, protective response to stresses such as invading microbes, strenuous exercise, anesthesia, and surgery
b. Leukopenia: An abnormally low level of white blood cells (below 5000/µL). It is never beneficial and may be caused by radiation, shock, and certain chemotherapeutic agents.
c. emigration (diapedesis): RBCs are contained within the bloodstream, but WBCs leave the bloodstream through this process. in which they roll along the endothelium, stick to it, and then squeeze between endothelial cells. The precise signals that stimulate emigration through a particular blood vessel vary for the different types of WBCs. Molecules known as adhesion molecules help WBCs stick to the endothelium. For example, endothelial cells display adhesion molecules called selectins in response to nearby injury and inflammation. Selectins stick to carbohydrates on the surface of neutrophils, causing them to slow down and roll along the endothelial surface. On the neutrophil surface are other adhesion molecules called integrins, which tether neutrophils to the endothelium and assist their movement through the blood vessel wall and into the interstitial fluid of the injured tissue.
d. Phagocytosis: neutrophils and macrophages are active in this process. They can ingest bacteria and dispose of dead matter.
e. Chemotaxis: Several different chemicals released by microbes and inflamed tissues attract phagocytes. The substances that provide stimuli for chemotaxis include toxins produced by microbes; kinins, which are specialized products of damaged tissues; and some of the colony-stimulating factors (CSFs). The CSFs also enhance the phagocytic activity of neutrophils and macrophages.
f. Lysozyme: Among WBCs, neutrophils respond most quickly to tissue destruction by bacteria. After engulfing a pathogen during phagocytosis, a neutrophil unleashes several chemicals to destroy the pathogen. These chemicals include this enzyme, which destroys certain bacteria, and strong oxidants, such as the superoxide anion (O2-), hydrogen peroxide (H2O2), and the hypochlorite anion (OCl-), which is similar to household bleach.
g. differential white blood cell count: a count of each of the five types of white blood
cells, to detect infection or inflammation, determine the effects of possible poisoning by chemicals or drugs, monitor blood disorders (for example, leukemia) and the effects of chemotherapy, or detect allergic reactions and parasitic infections. Because each type of white blood cell plays a different role, determining the percentage of each type in the blood assists in diagnosing the condition.
7. Describe the structure, function and origin of platelets.
A. platelets or thrombocytes: Besides the immature cell types that develop into erythrocytes and leukocytes, hemopoietic stem cells also differentiate into cells that produce these. Each fragment, enclosed by a piece of the plasma membrane, is a platelet. They break off from the megakaryocytes in red bone marrow and then enter the blood circulation. Between 150,000 and 400,000 are present in each microliter of blood. Each is irregularly disc-shaped, 2–4 µm in diameter, and has many vesicles but no nucleus.
I. Megakaryoblast: Under the influence of the hormone thrombopoietin, myeloid stem cells develop into megakaryocyte colony-forming cells that in turn develop into precursor cells called megakaryoblasts. Megakaryoblasts transform into megakaryocytes, huge cells that splinter into 2000 to 3000 fragments. [Show Less]